GB476821A - Improvements in and relating to liquid-blast electric circuit breakers - Google Patents

Abstract

476,821. Liquid - blast switches. BRITISH THOMSON-HOUSTON CO., Ltd. July 31, 1936, No. 21301. Convention date, Aug. 1, 1935. [Class 38 (v)] A circuit-breaker comprising fixed, intermediate, and movable tubular contacts coaoting in an explosion pot and arranged to form two breaks in series, the arc at one of the breaks creating pressure within the pot for driving a blast of quenching-liquid through the arc at the other break, has the intermediate contact provided with a passage for transmitting pressure from the pot to the interior of the tubular contact, thereby to cause preliminary acceleration of liquid in the path of the blast created by the pressure-generating arc prior to separation of the tubular and intermediate contacts. The fixed and intermediate contacts 1, 2 are mounted and guided in insulating plates 10, 15, respectively, and urged by springs 13, 14, respectively, in the direction of the tubular, movable contact 3. In opening circuit, contacts 1, 2 separate first and draw an arc in the pressure chamber 16, which arc acts by means of apertures 15<1> to drive a radial blast of oil (or other insulating or arc-extinguishing liquid) into the main arc produced in chamber 17 by the subsequent separation of 3 from 2. The latter has a passage 18 in alignment with the bore of 3, which passage allows the pressure in 16 to accelerate the oil in 3 before the main arc is formed, thus lowering the pressure therein and enabling the radial blast to be instantly accelerated to the velocity requisite for breaking the main arc as soon as it forms. Moreover, the passage 18 serves to minimize gas-formation and to relieve excessive pressures due to interruption of short circuits. The passage may, however, be provided with a valve which remains on its seating and enables sufficient pressure for extinguishing light-current arcs to be generated, but yields to relieve excess pressures and accelerate the oil blast in the case of heavy currents, Fig. 2 (not shown).. In Fig. 5, two passages are provided at 26 in the lower enlarged part of intermediate contact 2<11>, and apertures 31 in the movable contact 3 serve to decrease the resistance to quick acceleration of the blast. Contact 2<11> may be mounted, as shown, on an insulating plate 27 secured by insulated rods 28, or, Fig. 3 (not shown), it may be mounted on a plate 15 similar to that shown in Fig. 1. In Fig. 5, the fixed contact 1 is of magnetic material and is adapted to be attracted to a magnetic core 45 by the energization of a series coil 44, thereby initiating formation of the pressure-generating arc by light overloads, before the movable contacts 3 and bridge-member 41 are tripped open by the usual inverse time-limit relay. By thus building up pressure before the relay operates, a strong blast is assured with light currents, whereas with heavy currents the relay operates instantaneously to trip the breaker so that excessive pressure is not set up in the pot.